A magnetic recording device, for example, a hard disk drive, has gradually been expected to provide more storage capacity as the recent trend of the information society has demanded it. One way to increase the storage capacity of magnetic recording devices is to increase the recording density per unit area of the magnetic recording device, and improvement in techniques for increasing the sensitivity of a read device that utilizes the magnetoresistive effect and for narrowing a track width have been identified.
While magnetic signals on a recording medium have been converted into electric signals by using an anisotropic magnetoresistive effect (AMR) at a low recording density of several Gb/in2, a read device using a giant magnetoresistive effect (GMR) of higher sensitivity has been used for higher recording density than that described above. However, along with improvement of higher recording density, use of a high sensitive read device such as a GMR (CPP-GMR) or tunnel magnetoresistive effect (TMR) device of a CPP (current perpendicular to the plane) system in which a detection current flows in a perpendicular direction to the film plane is very useful. Further, for narrowing the track width, development has been made in regard to the technique of narrowing a resist dimension by exposure conditions in the mask pattern formation.
The CPP structure magnetoresistive head generally includes a problem that the portion of the magnetoresistive film tends to generate heat more than that in a CIP (current into the plane) structure magnetoresistive head. In the CIP structure head, since sense current flows in the in-plane direction of the stacked plane in the stacked film of the magnetoresistive sensor film, more sense current flows to a layer comprising a material of lower electric resistivity and less sense current flows to a material of higher electric resistivity in the layers constituting the magnetoresistive film. Generally, the material of lower electric resistivity described above is an intermediate layer (e.g., Cu) provided between two ferromagnetic layers which are an important part of generating the magnetoresistive effect, and flowing of a large sense current in this layer means producing a high output. Further, a material of higher electric resistivity is an anti-ferromagnetic layer, that is, an anti-ferromagnetic material or a permanent magnet material, and decrease in the sense current flowing therethrough means also the suppression of heat generation.
On the other hand, in the CPP structure magnetoresistive head, since a sense current flows through the stacked plane of a magnetoresistive film, an identical current flows basically to all of the layers. That is, when a large sense current flows to an intermediate layer provided between two ferromagnetic layers which are an important part for generating the magnetoresistive effect, an identical current flows also to the anti-ferromagnetic layer of high electric resistivity to result in large heat generation. In the case of a metal, since the electric resistivity increases along with a rise of temperature, the resistance of the magnetoresistive film of the CPP structure magnetoresistive head increases by the heat generation. Therefore, an MR ratio is lowered to lower the read output. FIG. 10 shows the temperature dependence of the MR ratio in a current CPP structure magnetoresistive head. In FIG. 10, the abscissa shows the temperature of a magnetoresistive film and the ordinate shows an MR ratio. As shown in FIG. 10, as the temperature of the magnetoresistive film rises, the MR ratio is lowered, and the MR ratio showing about 11.5% at 20° C. lowers to about 10% at 50° C. and lowers to about 8.5% at 120° C. Further, since an insulating film is disposed on each side and in a device height direction of the magnetoresistive film of the CPP structure, the magnetoresistive film being a heat generation source, such that the sense current flows to a magnetoresistive film, a heat dissipation efficiency is also poor.
Jap. Pat. Appl. No. JP-A 2004-5763, which is hereby incorporated by reference, describes that the heat of a GMR film can be dissipated effectively by disposing a heat dissipation layer by way of an insulative layer on the side opposite to the side facing the recording medium of a GMR film. Jap. Pat. Appl. No. JP-A 2004-335071, which is hereby incorporated by reference, describes that the generation of Joule heat can be decreased in a CPP-GMR head by a structure in which an anti-ferromagnetic layer of high electric resistivity is disposed on the lateral surface in a track width direction or on the lateral surface in the device height direction of a fixed magnetic layer, and an anti-ferromagnetic layer is not disposed in a main path of the sense current.